History of INFOMAR Surveys

The Lidar survey was completed in Lough Foyle in 2008 by Tenix. Depths were achieved from drying 50 metres to depths of 10 metres inside the Lough, and 30 metres seaward of the Lough. Operations were suspended once turbid conditions were encountered in the southern and south eastern parts of Lough Foyle.

Another Lidar survey was attempted in Inner Lough Foyle in 2010 by Pelydryn. However, no valid data was produced. Inner Lough Foyle, the southern half of the lough is mainly shallow mud flats with a deeper channel created by the River Foyle. The water column contained large amounts of suspended mud sediment resulting in poor conditions for laser operations.

Shaded Relief

The 3D appearance is achieved using software called Fledermaus. By using some vertical exaggeration, artificial sun-shading (usually as if there is a light source in the nw 315°) and colouring the depths using various colour maps, it is possible to highlight the subtle relief of the seabed. This helps us to quickly understand the variation in depths.

Shaded relief image of data collected in 2008 lidar survey. Gaps (white areas) in the data occurred where the laser technology used in lidar surveys could not penetrate through the entire water column due to the water being too deep or decreased clarity in the water. (Click image for more detail)

All of our Charts for Lough Foyle can be downloaded in pdf format from this page.

Backscatter

Multibeam Systems also collect additional information, including the strength of the acoustic signal (or return) from the seafloor. This is known as Backscatter. Differing seafloor types, such as mud, sand, gravel and rock will have different Backscatter values depending on the amount of energy they return to the sonar head. Rocky areas will typically have high returns while soft sediments like mud are more likely to absorb energy and have low Backscatter returns. These differing values are used to generate a grey-order image (i.e. dark for high returns, bright for low returns) of the seabed which can be used to examine the nature of the seafloor.

Overview backscatter image of the seabed surveyed off the Donegal coast. (Click on image for more detailed map)

Geology

Lough Foyle Geology

Lough Foyle is flanked on its western side by rocks of the Dalradian, an ancient group of metamorphic rocks that have experienced instense tectonic events in the distant past. On its eastern coast, mudstones and sandstones of the Triassic and Jurassic periods make up the bedrock, with younger igneous rocks found further along the coast as you exit the estuary and turn eastwards.